Is Donald Trump facing a credibility test as he continues to threaten Iran? For weeks, the U.S. President has spent weeks warning Iran’s leaders and promising support to protesters while deploying U.S. naval forces near Iran’s coast. Now, as the White House turns toward diplomatic talks in Istanbul, analysts caution Trump faces a credibility test if his threats are not enforced. By drawing a red line over Tehran’s violent crackdown and nuclear ambitions, Trump invites comparisons to Barack Obama’s 2013 Syria warning, when diplomacy replaced military strikes.